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Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuum and emission line flux variations observed through spectroscopic monitoring campaigns to infer the radius of the broad-line region (BLR) and, subsequently, the central black hole mass in type 1 AGNs. We present results from a multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from around the world. We measure BLR radii and black hole masses for six objects. The primary goal of this campaign was to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity AGNs. Using cross correlation techniques to measure the time delay between the mean optical continuum flux density around 5100 Å and the integrated Hβ flux, we determine the Hβ lags and black hole mass measurements listed in columns 2 and 3 of Table 1, respectively. Column 4 tells if this measurement is new, an improvement meant to replace a previous, less reliable measurement, or simply an additional measurement not used to replace a previous value. The complete results from this study are currently being prepared for publication. A subsequent velocity-resolved analysis of the Hβ response shows that three of the six primary targets demonstrate kinematic signatures (column 5) of infall, outflow, and non-radial virialized motions (see Denney et al. 2009).

Haemosporidian parasites are common in birds in which they act as an important selective pressure. While most studies so far have focused on the effect of their prevalence on host life-history traits, no study has measured the effect of parasitaemia. We developed molecular methods to detect, identify and quantify haemosporidia in 2 natural populations of the Blackbird Turdus merula. Three different parasite genotypes were found – 1 Haemoproteus and 2 Plasmodium. A PCR-RFLP screening revealed that only approximately 3% of blackbirds were free of parasites, compared to the 34% of uninfected birds estimated by blood smear screening. A quantitative PCR (q-PCR) assay revealed a weaker parasitaemia in microscopically undetected parasites compared to microscopically detected ones. Large parasitaemia differences were found between parasite species, suggesting either differing parasite life-histories or host resistance. Parasitaemias were also weaker in male hosts, and in urban habitats, suggesting that both host factors (e.g. immunity) and habitat characteristics (e.g. vector availability) may modulate parasite density. Interestingly, these differences in parasitaemia were comparable to differences in parasite prevalence estimated by smear screening. This suggests that previous results obtained by smear screening should be reinterpreted in terms of parasitaemia instead of parasite prevalence.

We discuss the discovery of six bright Lyman break galaxy candidates in the Sloan Digital Sky Survey and the follow-up observations necessary to determine whether they are powered by star formation or by active galactic nuclei.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Chemical mechanical polishing and stress corrosion cracking result from chemical attack at stressed regions. To better understand the combined effects of chemical attack and stress, a kinetic Monte Carlo (kMC) study of the formation of dislocation etch pits is being pursued. In the simulations, atoms from a diamond cubic lattice are irreversibly removed with a probability which depends on an atom's number of nearrest neighbors as well the local stress developed from its physical location with respect to a dislocation in the lattice. In accordance with experimental observations, both faceted and non-faceted dislocation etch-pits have been observed. Simulations have been performed for various values of the strength to the etchant attack and the magnitude of the stress produced by the dislocation.

The interfacial zone separating cement paste and aggregate in mortar and concrete is believed to influence many of the properties of these composites. This paper presents a theoretical framework for quantitatively understanding the influence of the interfacial zone on the overall electrical conductivity of mortar, based on realistic random aggregate geometries. These same ideas may also be used to approximately predict the fluid permeability of mortar.

Computer modelling of the properties and performance of cement-based materials is complicated by the large range of relevant size scales. Processes occurring in the nanometersized pores ultimately affect the performance of these materials at the structural level of meters and larger. One approach to alleviating this complication is the development of a suite of models, consisting of individual digital-image-based structural models for the calcium silicate hydrate gel at the nanometer level, the hydrated cement paste at the micrometer level, and a mortar or concrete at the millimeter level. Computations performed at one level provide input properties to be used in simulations of performance at the next higher level. This methodology is demonstrated for the property of ionic diffusivity in saturated concrete. The more complicated problem of drying shrinkage is also addressed.

X-ray microtomography can be used to generate three-dimensional 5123 images of random materials at a resolution of a few micrometers per voxel. This technique has been used to obtain an image of an ASTM C109 mortar sample that had been exposed to a sodium sulfate solution. The three-dimensional image clearly shows sand grains, cement paste, air voids, cracks, and needle-like crystals growing in the air voids. Volume fractions of sand and cement paste determined from the image agree well with the known quantities. Implications for the study of microstructure and proposed uses of X-ray microtomography on cement-based composites are discussed.

Previously, a hard core/soft shell computer model was developed to simulate the overlap and percolation of the interfacial transition zones surrounding each aggregate in a mortar or concrete. The aggregate particles were modelled as spheres with a size distribution representative of a real mortar or concrete specimen. Here, the model has been extended to investigate the effects of aggregate shape on interfacial transition zone percolation, by modelling the aggregates as hard ellipsoids, which gives a dynamic range of shapes from plates to spheres, to fibers. For high performance concretes, the interfacial transition zone thickness will generally be reduced, which will also affect their percolation properties. This paper presents results from a study of the effects of interfacial transition zone thickness and aggregate shape on these percolation characteristics.

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